Formation of the seminiferous cords, the precursor seminiferous tubules, is the first morphological event that distinguishes the testis from the ovary. The cords contain Sertoli and germ cells surrounded by peritubular cells. Sry expressed in the Sertoli cell induces mesonephric cell migration into the differentiating testis to form cords. If the mesonephros is removed, or mesonephric cell migration is blocked, no cord formation occurs. One cell type that migrates to the testis during cord forrnation is the endothelial cell. Therefore, angiogenic factors involved in vasculature development may also be critical for cord formation. [unreadable] [unreadable] The long-range goal of this research is to elucidate cellular and molecular mechanisms regulating angiogenesis and morphological sex determination (cord formation) in the testis. The objective of this proposal, the first step toward attaining our long-range goal, is to identify angiogenic factors that induce mesonephric endothelial cell migration and determine if these factors are participating in both vascular development and cord formation. Preliminary experiments, in our laboratory, have established that one angiogenic factor, Vascular Endothelial Growth Factor (VEGF), and its receptor VEGFR-2 are present at the time of cord formation in cells that direct testis differentiation. Furthermore, preliminary data from our lab have determined that signaling antagonists to VEGF receptors inhibit cord formation. Therefore, the central hypothesis of this proposal is that VEGF and VEGFR-2 are involved in both vascularization and cord formation in the testis. To test the hypothesis and accomplish the overall objective of this application two specific aims are proposed: 1) Determine the mechanisms of VEGF and VEGFR-2 action on cord formation and vascular development during testis morphogenesis; and 2) Investigate the functional effects of VEGF isoforms on endothelial cell migration during testis morphogenesis. Altered regulation of either VEGF or VEGFR-2 may result in abnormal testis differentiation resulting in infertility. The current proposal seeks to fill the gaps in our current knowledge of how VEGF and VEGFR-2 may regulate testis morphogenesis to gain a better understanding of male infertility problems occurring through abnormal testis differentiation. [unreadable] [unreadable] [unreadable]